This invention generally relates to liquid dispensing and, more specifically, to a multinozzle dispensing apparatus including nozzle adapters which provide rapid and selective shut-off or recirculation capability to the apparatus.
Hot melt thermoplastic adhesives have been widely used in industry for adhering many types of products, and are particularly useful in applications where quick setting time is desired. One popular application for hot melt adhesives for several years has been in the manufacture of absorbent hygienic articles such as disposable diapers, incontinence pads and similar articles. Hot melt adhesive may be used, for example, to bond the backing sheet to the nonwoven fibrous material of the article and also to adhere the fluff layer to the nonwoven cover sheet.
One apparatus commonly used in the manufacture of disposable diapers and other hygienic articles is a metering gearhead having a plurality of spaced discharge orifices, each supplied with adhesive from a gear pump. The discharge orifices are positioned relative to the backing sheet of a diaper, for example, to apply parallel rows of adhesive thereto for subsequent attachment of the nonwoven absorbent pad of the diaper. A similar apparatus may be used to adhere the fluff layer to the nonwoven cover sheet. The primary advantages of metering gearheads include precise control of the quantity of adhesive dispensed and accurate location of the adhesive on the substrate so that the resulting product has multiple rows of adhesive of uniform adhesive volume, as well as uniform width and spacing of the rows. However, liquid dispensing apparatus such as metering gearheads which utilize a number of spray nozzles to dispense a relatively wide path of adhesive also have some areas in need of improvement.
One disadvantage of prior dispensing apparatus for hot melt adhesives concerns the relatively large amount of time which must be spent changing over or modifying an apparatus to dispense rows of adhesive along a wider or narrower path. This may be required, for example, in applications in which a single manufacturing line is used for manufacturing products of different sizes. An example of this is in the case of diapers, where the same manufacturing line may be used to manufacture or assemble several different sizes of diapers. The various metering gearheads used on the line must be modified to dispense adhesive along a path having a width corresponding to a particular size of diaper.
In the past, in order to modify the manufacturing line to accommodate a different substrate size, at least a portion of each metering gearhead had to be completely replaced with components having the correct number of outlet orifices or nozzles arranged at the proper width for the substrate, or one or more of the outside nozzles had to be removed and replaced by a blocking plate to change the effective dispensing width of that gearhead. U.S. Pat. No. 4,983,109, assigned to the assignee of the present invention, and the disclosure of which is hereby fully incorporated by reference herein, discloses various types of such blocking plates which may be used to recirculate the adhesive into the conventional recirculation loop of the gearhead so that there are no dead-end passages created which might lead to charring.
Both of these prior changeover methods not only require undesirable amounts of down time for the production line, but also require the stocking of additional parts which may add to the expense and inconvenience of the changeover process. Furthermore, the areas of the production line in which such metering gearheads are typically mounted generally do not allow easy access to the nozzles with the tools required for changing from nozzles to backing plates and vice versa or to change the necessary gearhead components.
It would therefore be desirable to provide nozzles and a dispensing apparatus including one or more such nozzles which may be easily changed over from an operative dispensing condition to a recirculating condition without the need for tools and without the need for replacement parts such as blocking plates.